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Calculation of Critical Experiments involving U(37)02F2 Solution
K. L. Goluoglu and A. W. Krass
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6271, USA goluoglukl@ornl.govINTRODUCTION
Critical experiments were conducted at the Oak
Ridge Critical Experiment Facility (ORCEF) to
determine the critical concentration for an
unreflected 69.2-cm-diameter sphere of U02F2,
at an enrichment of -37 percent U235, by weight.
These experiments were a continuation of
previous efforts to determine critical dimensions
for fissile materials in simple geometry. Some
of the earlier experiments in this vessel have
been published as part of the OECD handbook.'
The reports concerning these experiments have
only recently become available. Until August
2005, Refs. 2 and 3 were still classified. 2,3
These documents, along with experimental
logbooks4 and unclassified papers available on
the experimental campaign and facility are being
used to generate a computer model for this
critical experiment.
BACKGROUND
A program to determine the critical conditions of
aqueous solutions of uranium salts enriched in
U235 was initiated in 1947. The experiments
were part of a long range program of ORNL
personnel at the ORCEF, and numerous reports
document the results of these experiments. The
particular series of experiments dealt with in this
paper were performed between 1958 and 1960.
The experiments being analyzed involve a
U(37)02F2 solution in a sphere. The uranium
was enriched to -37 percent U235 by weight. The
vessel was constructed of aluminum, with an
inside diameter of 69.20 cm and a wall thickness
of 0.64 cm. The sphere was unreflected, and was
the same sphere used for the experiments
originally reported in ORNL-26095 and later
analyzed in the OECD report HEU-SOL-
THERM-013.6 The measured volume of the
tank was 173.6 L.
The U(37)02F2 concentration in the solution was
adjusted such that when the aluminum vessel
was completely filled the multiplication factor
was greater than unity and the excess reactivitywas measured by means of a positive reactor
period. The final solution used to achieve
criticality had a density of 1.057 g/cm3. The
solution contained 49.19 mg of U/g of solution.
The U235 content reported was 36.96 wt%. This
value has some uncertainty associated with it,
which is noted in the Y-12 reports. The U235
density is reported as 19.19 mg/cm3, with a total
mass of 3331 g. The reported H:U235 ratio is
1343.
The experimental keff for the critical sphere was
measured to be 1.0011. The experimenters also
published an adjusted keff to represent the critical
mass only, to account for small differences
between an idealized system and the physical
reality of the experiment. The adjustment
accounts for things such as the small amount
solution in the polar port of the sphere and the
aluminum walls of the sphere. The
experimenters compared their calculated values
for a solution in an idealized aluminum shell to
the 1.0011 measurement.
CURRENT RESULTS AND FUTURE
WORK
Preliminary calculations for this system have
been performed with the CSAS25 control
module of the SCALE 5.0 code system.7
Calculations were performed using either
NITAWL or CENTRM for cross-section
processing. 16-energy-group Hansen-Roach and
238-energy-group ENDFB-VI cross sections
were used. The results are shown in Table 1.
The results shown in Table 1 are for a simple
case, and do not model the structure or room of
the experiment other than the aluminum tank.
The calculated results by the experimenters, ca.
1973, using Hansen-Roach cross-sections and
ANISN, show a similar under-prediction of keff
when calculating the solution sphere in the
aluminum shell (keff=1.0005).
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Goluoglu, K.L. Calculation of Critical Experiments involving U(37)O2F2 Solution, report, March 3, 2006; [Tennessee]. (https://digital.library.unt.edu/ark:/67531/metadc874555/m1/1/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.